Tropical Depression 05W Update #1

Invest 90W has been upgraded to a tropical depression earlier this morning by both JTWC and JMA. TD 05W was last located approximately 470km south of Guam or about 760km east of Yap Island. Maximum sustained winds are at 45kph with gusts of up to 65kph. TD 05W is currently moving west northwestward at 20kph.

IR Image from RAMMB-CIRA

We have been watching 90W (now 05W) for days now and we keep mentioning the cyclic nature of the storm in terms of development. The storm is still largely being influenced by diurnal variations and can't quite intensify at a consistent pace. Latest IR image shows warmer cloud tops compared to earlier this morning with new 'how' towers forming near the center. We will probably see another round of strong convective activity later tonight. While it does look weak, the system is still somewhat organized with weak banding and good outflow. The latest wind analysis from JTWC is supported by satellite data taken earlier today showing winds of 35 to 55kph winds near the center.

Computer models are divided regarding 05W's future. A number of models are trying to develop the system into a strong cyclone although a couple of other models (GFS and ECMWF, for example) are not showing a strong solution and instead keeps 05W very weak as it traverses the Western Pacific. JWTC, on the other hand, is very aggressive in terms of intensity forecast--expecting 05W to become a strong typhoon by Thursday. As for the track, preliminary thoughts based on models and satellite data, suggest that 05W won't hit the Philippines. It will, however, enter the Philippine Area of Responsibility by as early as Thursday. PAGASA will assign the local name "Butchoy" once it enters the PAR.

Forecast Track (NOT OFFICIAL!)

Our forecast takes into account the uncertainty among computer models as well as the aggressive forecast from JTWC. We think Tropical Depression 05W will remain weak for another 24 hours as it tries to sort out the development cycles. It could become a tropical storm by Wednesday as it passes 250km north of Yap Island. A subtropical ridge anchored south of Japan will keep 05W at a generally westward course. It will then start turning to the northwest by Thursday and eventually to the north by Friday as it rounds the ridge. By that time, 05W will be far away from Luzon to really cause any stormy conditions. Nevertheless, there is still a slight chance that 05W will move closer than our initial forecast. If it stays weak enough, it will continue moving more to the west; JTWC has actually shifted their track a little bit to the west. Our intensity forecast is weaker than that of JTWC but we are still expecting 05W to strengthen into a Typhoon as it moves across the warm waters of the Philippine Sea.

We'll have another update tomorrow.
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Issued (0830 UTC) 430pm PhT 061112